Laser etching method and apparatus therefor

ABSTRACT

The invention provides a laser etching method for optical ablation working by irradiating a work article formed of an inorganic material with a laser light from a laser oscillator capable of emitting in succession light pulses of a large energy density in space and time with a pulse radiation time not exceeding 1 picosecond, wherein, in laser etching of the work article formed of the inorganic material by irradiation thereof with the laser light from the laser oscillator with a predetermined pattern and with a predetermined energy density, there is utilized means for preventing deposition of a work by-product around the etching position.

This application is a division of U.S. application Ser. No. 09/717,242filed on Nov. 22, 2000, now U.S. Pat. No. 6,861,364.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser etching method and a laseretching apparatus for working an article with a laser beam, and moreparticularly to a laser etching method and a laser etching apparatuscapable, in working the article of an inorganic substance, of workingwithout generating deposition around the etching position, and adaptedfor fine working of a material for a micromachine, an IC or a diodedevice.

2. Related Background Art

In fine working of a structural member by laser working, it is customaryto utilize a harmonic wave of an excimer laser or a YAG laser.

However, as the energy density of the laser light in the oscillatedpulse is limited to a level of 100 megawatts at maximum, such laserworking method is hardly applicable to an article formed of an inorganicmaterial and is only applicable to the sublimation ablation working ofarticles principally composed of organic materials. For this reason, thefine working of the article formed of inorganic materials has beenachieved by a lithographic process including steps of resist coating,resist patterning by exposure, resist development, etching utilizing theresist pattern and resist ashing for each material, but such process isassociated with drawbacks of an increased cost resulting from thecomplex process steps and a large investment for the production facilityin consideration of the process tact time.

In order to resolve such drawbacks, the present applicant proposes, forexample in the Japanese Patent Application No. 11-316760, a laserworking method for fine working of a structure in an article formed ofinorganic materials by sublimation ablation working, utilizing a featurethat the laser light emitted from a laser oscillator with a pulseemission time of 1 picosecond or less has a drastically high energydensity in time and a feature that the laser light is not converted intothermal energy but is directly converted into a lattice bond cleavingenergy because of the very short laser irradiation time.

However the above-mentioned laser working method for sublimationablation working is capable of etching the article formed of theinorganic material by ablation sublimation, but, in certain materials,the sublimated and gasified atoms or molecules instantly causerecombination, thereby being liquefied and deposited in the etchingposition in the vicinity thereof-and solidified, whereby the vicinity ofthe etching position cannot be maintained clean or the etching itselfcan be prevented by the deposition of such by-products.

Such drawbacks become particularly conspicuous in materials incrystalline or amorphous solid state by covalent bonds. The cause forsuch phenomenon is not yet clarified, but is considered to be inherentto the materials having covalent bonds of a higher bonding energy, sincethe above-mentioned drawbacks are not conspicuous in the crystallinematerials based on metal bonding or ionic bonding or in the amorphousmaterials based on ionic bonding.

SUMMARY OF THE INVENTION

In consideration of the foregoing, the object of the present inventionis to provide a laser etching method and a laser etching apparatuscapable, in laser etching of an article formed of an inorganic material,of working without deposition around the etching position and of fineworking for a material of a micromachine, an IC or a diode device.

The above-mentioned object can be attained, according to the presentinvention, by a laser etching method and a laser etching apparatusconstructed as described in the following (1) to (35):

-   (1) A laser etching method for optical ablation working by    irradiating a work article formed of inorganic materials with a    laser light from a laser oscillator capable of emitting in    succession light pulses of a large energy density in space and time    with a pulse radiation time not exceeding 1 picosecond:

wherein, in laser etching of the work article formed of the inorganicmaterial by irradiation thereof with the laser light from the laseroscillator with a predetermined pattern and with a predetermined energydensity, there is utilized means for preventing deposition of a workby-product around the etching position.

-   (2) A laser etching method according to (1), wherein the means for    preventing deposition of the work by-product around the etching    position is adapted for working the work article by irradiation with    the laser light, by intermittent irradiation with an interval longer    than the oscillation frequency of a pulsed laser.-   (3) A laser etching method according to (1), wherein the means for    preventing deposition of the work by-product around the etching    position is adapted for working the work article by irradiation with    the laser light, in a state where a gas flow is generated in the    work position of the work article.-   (4) A laser etching method according to (3), wherein the gas flow in    the work position of the work article is an air flow.-   (5) A laser etching method according to (3), wherein the gas flow in    the work position of the work article is a nitrogen flow.-   (6) A laser etching method according to (1), wherein the means for    preventing deposition of the work by-product around the etching    position is adapted for working the work article by irradiation with    the laser light, by executing laser light irradiation in a state    where the work article is positioned in an atmosphere other than    air.-   (7) A laser etching method according to (6), wherein the atmosphere    other than air is gas of an atomic weight smaller than that of    nitrogen molecule.-   (8) A laser etching method according to (7), wherein the gas is    helium gas.-   (9) A laser etching method according to (7), wherein the gas is    hydrogen gas.-   (10) A laser etching method according to (6), wherein the atmosphere    other than air is liquid of which medium transmits the laser light.-   (11) A laser etching method according to (10), wherein the liquid    transmitting the laser light is water.-   (12) A laser etching method according to (10), wherein the liquid    transmitting the laser light is silicone oil.-   (13) A laser etching method according to (1), wherein the means for    preventing deposition of the work by-product around the etching    position is adapted for working the work article by irradiation with    the laser light, in a state where the work article is heated to    200° C. or higher.-   (14) A laser etching method according to (1), wherein the means for    preventing deposition of the work by-product around the etching    position is adapted for working the work article by irradiation with    the laser light, in a state where the work article is provided in a    gaseous atmosphere not exceeding 10 Torr.-   (15) A laser etching method according to (1), wherein the inorganic    material is a crystal of covalent bond.-   (16) A laser etching method according to (1), wherein the inorganic    material is crystal or amorphous silicon.-   (17) A laser etching method according to (1), wherein the inorganic    material is a silicon compound.-   (18) A laser etching method according to (1), wherein the laser    oscillator has a spatial compression device for light propagation.-   (19) A laser etching method according to (18), wherein the spatial    compression device for light propagation comprises chirping pulse    generation means and vertical mode synchronization means utilizing    the optical wavelength dispersing characteristics.-   (20) A laser etching apparatus provided with from a laser oscillator    capable of emitting in succession light pulses of a large energy    density in space and time with a pulse radiation time not exceeding    1 picosecond and adapted for optical ablation working of a work    article formed of inorganic materials by irradiation of the work    article with a laser light from the laser oscillator with a    predetermined pattern and with a predetermined energy density, the    apparatus comprising:

means for preventing deposition of a work by-product around the etchingposition for laser etching by irradiation of the work article formed ofthe inorganic material.

-   (21) A laser etching apparatus according to (20), wherein the means    for preventing deposition of the work by-product around the etching    position is means including a mechanical shutter for achieving    intermittent irradiation with an interval longer than the    oscillation frequency of a pulsed laser by controlling the laser    light from the laser oscillator by open/close control, thereby    working the work article.-   (22) A laser etching apparatus according to (20), wherein the means    for preventing deposition of the work by-product around the etching    position includes means for causing a gas flow in the work position    of the work article formed of the inorganic material, and adapted    for working the work article by irradiating the work article with    the laser light in a state where the gas flow is caused in the work    position of the work material formed of the inorganic material.-   (23) A laser etching apparatus according to (22), wherein the means    for causing the gas flow in the work position of the work article is    adapted to cause an air flow.-   (24) A laser etching apparatus according to (22), wherein the means    for causing the gas flow in the work position of the work article is    adapted to cause a nitrogen flow.-   (25) A laser etching apparatus according to (20), wherein the means    for preventing deposition of the work by-product around the etching    position is means for working the work article includes a chamber    and a light transmitting member capable of closing the chamber, and    is adapted to work the work article formed of the inorganic material    by positioning the work article in the chamber filled with a medium    other than air and closed by the light transmitting member, and    irradiating the work article with the laser light through the light    transmitting member.-   (26) A laser etching apparatus according to (25), wherein the medium    filled in the chamber other than air is gas of an atomic weight    smaller than that of nitrogen molecule.-   (27) A laser etching apparatus according to (26), wherein the gas is    helium gas.-   (28) A laser etching apparatus according to (26), wherein the gas is    hydrogen gas.-   (29) A laser etching apparatus according to (25), wherein the medium    filled in the chamber other than air is liquid capable of    transmitting the laser light.-   (30) A laser etching apparatus according to (29), wherein the liquid    transmitting the laser light is water.-   (31) A laser etching apparatus according to (29), wherein the liquid    transmitting the laser light is silicone oil.-   (32) A laser etching apparatus according to (20), wherein the means    for preventing deposition of the work by-product around the etching    position is includes a heater to be controlled at a predetermined    temperature by temperature adjusting means and is adapted for    working the work article by maintaining the work article formed of    the inorganic material at the predetermined temperature and    irradiating the work article with the laser light.-   (33) A laser etching apparatus according to (20), wherein the means    for preventing deposition of the work by-product around the etching    position includes a chamber and a light transmitting member capable    of closing the chamber, and is adapted for working the work article    formed of the inorganic material by irradiation with the laser    light, by positioning the work article in the chamber evacuated to a    pressure to a pressure not exceeding 10 Torr and closed by the light    transmitting member and irradiating the work article with the laser    light through the light transmitting member.-   (34) A laser etching apparatus according to (20), wherein the laser    oscillator has a spatial compression device for light propagation.-   (35) A laser etching apparatus according to (34), wherein the    spatial compression device for light propagation includes chirping    pulse generation means and vertical mode synchronization means    utilizing the optical wavelength dispersing characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the laser etching method in an embodiment 1 ofthe present invention;

FIG. 2 is a view showing the sequence of the laser irradiation method inthe embodiment 1 of the present invention;

FIG. 3 is a view showing the work state of a conventional laser etchingmethod as comparison;

FIG. 4 is a view showing the work state of the laser etching method ofthe embodiment 1 of the present invention;

FIG. 5 is a view showing the laser etching method in an embodiment 2 ofthe present invention;

FIG. 6 is a view showing the laser etching method in an embodiment 3 ofthe present invention;

FIG. 7 is a view showing the laser etching method in an embodiment 4 ofthe present invention; and

FIG. 8 is a view showing the laser etching method in an embodiment 5 ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention, in the embodiments based on the foregoingconfigurations, allows laser etching of a work article formed of aninorganic material without generating deposits around the etchingposition.

In a first embodiment, the irradiation of the work article is executedwith intermittent irradiation including an irradiation pause time or aninterval longer than the oscillation frequency of the pulsed laser,thereby avoiding deposition around the etching position and enablingfine working of the material for a micromachine, an IC or a diodedevice.

The atomic or molecular particles released by ablation generates aplasma cloud around the etching position, and such plasma cloud preventsthe emission of the atomic or molecular particles by ablation if theworking is continuously executed. Thus the sublimated material liquefiesor solidifies in the vicinity of the working position, thereby forming adeposit around the etching position.

On the other hand, in the above-described configuration utilizing theintermittent irradiation of the work article with the interval longerthan the oscillation frequency of the pulsed laser, an etching pausetime is provided after the etching for a predetermined duration so thatthe etching is re-started after the plasma cloud of the atomic ormolecular particles is scattered. It is thus rendered possible to hinderdeposition around the etching position, thereby avoiding generation ofsolid deposit around the etching position.

Also in a second embodiment, the working is executed in a state where agas flow is caused in the work position of the work article, therebypreventing deposition around the etching position and enabling fineworking of the material for a micromachine, an IC or a diode device. Theaforementioned atomic or molecular particles released by ablation remainless in the vicinity of the work position by collision with and removalby the gas flow from the work position, whereby prevented is thegeneration of solid deposit around the etching position.

Also in a third embodiment, the working by the laser light is executedin a state where the work article is positioned in an atmosphere otherthan air, thereby preventing deposition around the etching position andenabling fine working of the material for a micromachine, an IC or adiode device.

1) In case helium is employed for forming the atmosphere other than air,the atomic or molecular particles released by ablation show littlechange in the proceeding direction even in case of collision with thehelium atoms of a low atomic weight, thereby tending to move straightand remaining less in the vicinity of the etching position, wherebyprevented is the generation of solid deposit around the etchingposition.

2) In case hydrogen gas is employed for forming the atmosphere otherthan air, a particular advantage can be obtained in case the workarticle is composed of silicon, in addition to the above-mentionedeffect relating to the atomic weight, though danger in handlingincreases. The silicon atoms released by ablation chemically combinewith the hydrogen atoms to be converted into siline gas (SiH₄) which isgaseous and stable and is hardly deposited around the etching position,whereby prevented is the generation of solid deposit around the etchingposition.

3) In case water is employed for forming the atmosphere other than air,the atomic or molecular particles released by ablation are preventedfrom deposition in the vicinity of the etching position by the presenceof the water molecules and are fetched in such water molecules, thusbeing prevented from re-deposition, whereby prevented is the generationof solid deposit around the etching position. In this case, however, itis required that the optical absorbance of the work article is higherthan that of water and that a gaseous by-product is not generated byablation (because a gaseous by-product, if generated, remains as abubble in the working position because of the high surface tension ofwater, thereby hindering the light passing by refraction and disablingthe high precision working.

4) In case silicone oil is employed for forming the atmosphere otherthan air, the atomic or molecular particles released by ablation areprevented from deposition in the vicinity of the etching position by thepresence of the silicone oil molecules and are fetched in such siliconeoil molecules, thus being prevented from re-deposition, wherebyprevented is the generation of solid deposit around the etchingposition. In this case, however, it is required that the opticalabsorbance of the work article is higher than that of silicone oil (agaseous by-product, if generated by ablation, can be tolerated as itdoes not remain in a state stuck to the work article because of the lowsurface tension of silicone oil, and can be removed from the workarticle by a flow caused by the liquid pressure if the viscosity of thesilicone oil based on the molecular weight thereof is maintained low).

It is thus rendered possible to prevent solid deposit around the etchingposition by forming various atmospheres other than air as explained inthe foregoing 1) to 4).

Also in a fourth embodiment, the working is executed in a state wherethe work article is heated to 200° C. or higher, thereby preventingdeposition around the etching position and enabling fine working of thematerial for a micromachine, an IC or a diode device. The aforementionedatomic or molecular particles released by ablation require a longer timefor cooling and liquefaction by the heat from the heated inorganicmaterial, and liquefy or solidify by cooling from the air in a positiondistant from the inorganic material constituting the work article in thecourse of flight, thereby hindering solid deposition in the vicinity ofthe etching position, whereby prevented is the generation of soliddeposit around the etching position.

Also in a fifth embodiment, the working is executed in a state where thework article is maintained in an atmosphere of a pressure not exceeding10 Torr, thereby preventing deposition around the etching position andenabling fine working of the material for a micromachine, an IC or adiode device. The aforementioned atomic or molecular particles releasedby ablation fly in a space of a low pressure with a fewer number ofmolecules or atoms and show a lower probability of collision between theparticles and a longer average flight length, thereby tending to movestraight and remaining less in the vicinity of the etching position,whereby prevented is the generation of solid deposit around the etchingposition.

In the following the present invention will be clarified in detail bypreferred embodiments thereof.

[Embodiment 1]

At first reference is made to FIG. 1 for outlining the working method ofan embodiment 1 of the present invention. A laser light 1, emitted froman unrepresented laser oscillator, capable of emitting the laser lightwith an extremely short pulse emission time (not exceeding 1picosecond), after being modulated by a mechanical shutter 4-1 into apulse train 5-1 of laser light cut in time, illuminates a photomask 6,and the light transmitted by a mask pattern 8 is projected and focusedthrough a projection lens 7. The projected image is focused on thesurface of a work article 2 formed of an inorganic material.

The laser light 1 is irradiated in pulses in such state to effectsublimation ablation working of the work article 2, and, in the presentembodiment, the laser light irradiation is controlled by the open/closecontrol of the mechanical shutter 4-1 to etch the work article 2 in anintermittent sequence.

In the working method of the present embodiment, the intermittent laserirradiation etching was executed by employing a laser light of awavelength of 775 nm, a laser pulse oscillation frequency of 1 kHz, alaser irradiation pulse duration of about 150 femtoseconds, an opticalenergy of about 7μ joules per pulse concentrated in an area of 20 μm φthrough the photomask 6 and the projection lens 7, namely under a laserirradiating condition with an energy density of 15 terawatt/cm² perpulse, on a silicon crystal in the air of normal temperature and normalpressure wherein a cycle of on-state for 0.1 seconds (about 100 laserpulses are irradiated by the train of laser pulses: X) and off-state for0.5 seconds (the laser pulses are not irradiated: Y) are repeated 5times by the mechanical shutter 4-1 thereby giving about 500 laserpulses in total to form an etched hole of a depth of about 30 μm.

The working according to the present embodiment allows to achieve cleanetching without deposit around the worked hole, as shown in FIG. 4.

On the other hand, in case the silicon crystal was continuously etchedin the air of normal temperature and normal pressure with the totallaser irradiation pulses of about 500 pulses under the laser irradiatingcondition same as above and with the mechanical shutter 4-1 in theon-state (non-shielded state) for 0.5 seconds, the etched hole showed adepth of about 30 μm, but liquefied silicon was deposited in solidaround the worked hole as shown in FIG. 3. The solidified silicon couldnot be removed easily by mere rinsing with running water.

In comparison with the continuous etching method, the working method ofthe present embodiment allows to form an extremely clean worked holewithout deposit.

[Embodiment 2]

Now reference is made to FIG. 2 for outlining the working method of thepresent embodiment. A laser light 1, emitted from an unrepresented laseroscillator, capable of emitting the laser light with an extremely shortpulse emission time (not exceeding 1 picosecond), illuminates aphotomask 6, and the light transmitted by a mask pattern 8 is projectedand focused through a projection lens 7. The projected image is focusedon the surface of a work article 2 formed of an inorganic material.

On the other hand, a gas nozzle 4-2 emits nitrogen gas 5-2 in adirection indicated by an arrow whereby a gas flow is generated on thesurface of the work article 2. The laser light 1 is irradiated in pulsesto effect sublimation ablation working of the work article 2.

In the working method of the present embodiment, the continuous etchingwas executed, by employing a laser light of a wavelength of 775 nm, alaser pulse oscillation frequency of 1 kHz, a laser irradiation pulseduration of about 150 femtoseconds, an optical energy of about 7μ joulesper pulse concentrated in an area of 20 μm φ through the photomask 6 andthe projection lens 7, namely under a laser irradiating condition withan energy density of 15 terawatt/cm² per pulse, on a silicon crystal inthe air of normal temperature and normal pressure under an irradiationof 0.5 seconds for giving about 500 laser pulses in total and under anitrogen gas blow of about 1 m/sec to form an etched hole of a depth ofabout 30 μm.

The working method of the present embodiment under nitrogen gas blowingto the silicon crystal allows to achieve clean etching without depositaround the worked hole, as shown in FIG. 4. On the other hand, in casethe silicon crystal was etched in the air atmosphere without the gasblowing shows liquefied silicon deposited in solid around the workedhole as shown in FIG. 3. The solidified silicon could not be removedeasily by mere rinsing with running water. In comparison with theworking in the still air atmosphere, the working method of the presentembodiment allows to form an extremely clean worked hole withoutdeposit. Also the optimum rate of the gas flow is considered variableaccording to the size of the working area and the working speeddepending on the laser irradiation energy.

[Embodiment 3]

Now reference is made to FIG. 6 for outlining the working method of thepresent embodiment. A laser light 1, emitted from an unrepresented laseroscillator, capable of emitting the laser light with an extremely shortpulse emission time (not exceeding 1 picosecond), illuminates aphotomask 6, and the light transmitted by a mask pattern 8 is projectedand focused through a projection lens 7. The projected image is focusedon the surface of a work article 2 formed of an inorganic material.

The work article 2 is closed in a chamber 3 and a window 4-3 closing thechamber 3 and the space around the work article 2 is filled with a workarticle atmosphere material 5-3. In such state, the laser light 1 isirradiated in pulses to execute sublimation ablation etching of the workarticle 2.

In the working method of the present embodiment, the work article 2 wascomposed of crystalline silicon, and the chamber 3 was filled withhelium gas of normal pressure as the work article atmosphere material5-3.

In the working method of the present embodiment, the continuous etchingwas executed, by employing a laser light of a wavelength of 775 nm, alaser pulse oscillation frequency of 1 kHz, a laser irradiation pulseduration of about 150 femtoseconds, an optical energy of about 7μ joulesper pulse concentrated in an area of 20 μm φ through the photomask 6 andthe projection lens 7, namely under a laser irradiating condition withan energy density of 15 terawatt/cm² per pulse, on a silicon crystalunder an irradiation for 0.5 seconds for giving about 500 laser pulsesin total to form an etched hole of a depth of about 30 μm.

The working method of the present embodiment, in case of workingcrystalline silicon in a helium gas atmosphere, allows to achieve cleanetching without deposit around the worked hole, as shown in FIG. 4.

On the other hand, in case the crystalline silicon was etched in the airatmosphere shows liquefied silicon deposited in solid around the workedhole as shown in FIG. 3. The solidified silicon could not be removedeasily by mere rinsing with running water. In comparison, the workingmethod of the present embodiment allows to form an extremely clean.

Furthermore such working is not restrictive, and an extremely clean holecan also be obtained in case of:

employing silicon as the work article 2 and hydrogen gas as the workarticle atmosphere material 5-3; or

employing silicon as the work article 2 and silicone oil as the workarticle atmosphere material 5-3; or

employing gallium-arsine as the work article 2 and helium gas as thework article atmosphere material 5-3; or

employing gallium-arsine as the work article 2 and water as the workarticle atmosphere material 5-3; or

employing gallium-arsine as the work article 2 and silicone oil as thework article atmosphere material 5-3.

[Embodiment 4]

Now reference is made to FIG. 7 for outlining the working method of thepresent embodiment. A laser light 1, emitted from an unrepresented laseroscillator, capable of emitting the laser light with an extremely shortpulse emission time (not exceeding 1 picosecond), illuminates aphotomask 6, and the light transmitted by a mask pattern 8 is projectedand focused through a projection lens 7. The projected image is focusedon the surface of a work article 2 formed of an inorganic material.

On the other hand, the work article 2 is heated, by a heater 4-4 and thetemperature is measured by a thermometer 5-4. A constant temperature ismaintained by turning on and off the heater 4-4 by an unrepresentedtemperature controller.

The laser light 1 is irradiated in pulses in such state to effectsublimation ablation working of the work article 2.

In the working method of the present embodiment, the continuous laserirradiation etching was executed by employing a laser light of awavelength of 775 nm, a laser pulse oscillation frequency of 1 kHz, alaser irradiation pulse duration of about 150 femtoseconds, an opticalenergy of about 7μ joules per pulse concentrated in an area of 20 μm φthrough the photomask 6 and the projection lens 7, namely under a laserirradiating condition with an energy density of 15 terawatt/cm² perpulse, on a silicon crystal constituting the work article 2 in a statewhere the temperature is maintained at about 250° C. with a radiation of0.5 seconds for giving about 500 laser pulses in total to form an etchedhole of a depth of about 30 μm.

The working of the present embodiment employing crystalline silicon inthe state heated at 250° C. allows to achieve clean etching withoutdeposit around the worked hole, as shown in FIG. 4.

On the other hand, in case the silicon crystal was etched at the normaltemperature, liquefied silicon was deposited in solid around the workedhole as shown in FIG. 3. The solidified silicon could not be removedeasily by mere rinsing with running water. Thus, in comparison withworking at the normal temperature, the working method of the presentembodiment allows to form an extremely clean worked hole withoutdeposit. The deposit tended to decrease as the temperature ofcrystalline silicon becomes higher from the normal temperature (23° C.),but the deposit remained at a temperature less than 200° C.

[Embodiment 5]

Now reference is made to FIG. 8 for outlining the working method of thepresent embodiment. A laser light 1, emitted from an unrepresented laseroscillator, capable of emitting the laser light with an extremely shortpulse emission time (not exceeding 1 picosecond), after being modulatedby a mechanical shutter 4-1 into a pulse train 5-1 of laser light cut intime, illuminates a photomask 6, and the light transmitted by a maskpattern 8 is projected and focused through a projection lens 7. Theprojected image is focused on the surface of a work article 2 formed ofan inorganic material.

On the other hand, the work article 2 is enclosed by a chamber 3 and awindow 4-5 capable of transmitting light, and the space around the workarticle 2 is filled with reduced pressure air 5-5 of which pressure isreduced to 10 Torr or less by an unrepresented pump. The laser light 1is irradiated in pulses in such state to effect sublimation ablationworking of the work article 2.

In the working method of the present embodiment, the continuous laserirradiation etching was executed by employing a laser light of awavelength of 775 nm, a laser pulse oscillation frequency of 1 kHz, alaser irradiation pulse duration of about 150 femtoseconds, an opticalenergy of about 7μ joules per pulse concentrated in an area of 20 μm φthrough the photomask 6 and the projection lens 7, namely under a laserirradiating condition with an energy density of 15 terawatt/cm² perpulse, on a silicon crystal for a period of 0.5 seconds in the air of apressure of 5 Torr thereby giving about 500 laser pulses in total toform an etched hole of a depth of about 30 μm.

The working of the present embodiment, in case of working crystallinesilicon in the air of a pressure of 5 Torr, allows to achieve cleanetching without deposit around the worked hole, as shown in FIG. 4.

On the other hand, in case the crystalline silicon was etched in the airof normal pressure, liquefied silicon was deposited in solid around theworked hole as shown in FIG. 3. The solidified silicon could not beremoved easily by mere rinsing with flowing water. Thus, in comparisonwith the working in the air of normal pressure, the working method ofthe present embodiment allows to form an extremely clean worked holewithout deposit. The deposit tended to decrease as the pressure of theatmosphere around the crystalline silicon becomes lower from the normalpressure (760 Torr), but the deposit remained at a pressure exceedingabout 10 Torr.

As explained in the foregoing, the present invention provides a laseretching method and a laser etching apparatus capable, in laser etchingof a work article formed of an inorganic material, of working withoutdeposition around the etching position, and capable of fine working of amaterial for a micromachine, an IC or a diode device.

In a configuration of the present invention wherein the irradiation ofthe work article is executed with intermittent irradiation with aninterval longer than the oscillation frequency of the pulsed laser, anetching pause time can be provided after predetermined etching torealize a working sequence in which the etching is re-started after theplasma cloud consisting of atomic or molecular particles is scattered,whereby extremely clean working is made possible without deposit aroundthe etching position, as encountered i the conventional continuousetching operation.

In a configuration of the present invention wherein the working isexecuted in a state where a gas flow is generated in the workingposition of the work article, the atomic or molecular particles emittedby ablation are excluded from the work position by collection with thegas flow and remain less in the vicinity of the etching position,whereby extremely clean working is made possible without deposit aroundthe etching position.

Also in the present invention, by employing helium gas for forming anatmosphere other than air, the atomic or molecular particles emitted byablation can be made to proceed straight without remaining in thevicinity of the etching position, whereby working can be achievedwithout deposit around the etching position.

Also in the present invention, by employing hydrogen gas for forming anatmosphere other than air, particularly in case the work article iscomposed of silicon, it is made possible to convert the silicon atoms ina gaseous stable state, in addition to the aforementioned effect,whereby working can be achieved without deposit around the etchingposition.

Also in the present invention, by employing water for forming anatmosphere other than air, the atomic or molecular particles emitted byablation are fetched in water and prevented from re-deposition, wherebyworking can be achieved without deposit around the etching position.

Also in the present invention, by employing silicone oil for forming anatmosphere other than air, the atomic or molecular particles emitted byablation are fetched in silicone oil and prevented from re-deposition,whereby working can be achieved without deposit around the etchingposition.

Also in a configuration of the present invention wherein the irradiationof the work article is executed in a state where the work article isheated to 200° C. or higher, the atomic or molecular particles emittedby ablation require a longer time for cooling and liquefaction by theheat from the heated inorganic material and are liquefied or solidifiedin a position distant from the inorganic material constituting the workarticle by cooling from the air during the flight, whereby the soliddeposition around the etching position is reduced.

Also in a configuration of the present invention wherein the working ofthe work article is executed in a state where the work article ispositioned in a gaseous atmosphere of a pressure not exceeding 10 Torr,the atomic or molecular particles emitted by ablation fly in a space ofa low pressure with a fewer number of atomic or molecular particles andshow a lower probability of collision between the particles, therebyincreasing the average flight path and less subjected to the changes inthe proceeding direction, whereby the particles tend to proceed straightand remain less in the vicinity of the etching position to achieveextremely clean working without deposit around the etching position.

Furthermore, the foregoing five embodiments may be combined to presentdeposition in the vicinity of the work area.

For example, there may be adopted a combination of the first embodiment(intermittent laser irradiation), the second embodiment (gas flowblowing) and the fourth embodiment (heating of work article), or acombination of the third embodiment (gaseous atmosphere) and the fourthembodiment (heating of work article), or a combination of the firstembodiment (intermittent laser irradiation) and the fifth embodiment(reduced pressure atmosphere).

1. A laser etching method for optical ablation working by irradiating awork article formed by an inorganic material with a femtosecond laserlight emitted in successive trains of light pulses, the laser etchingmethod comprising: an etching step of laser etching the work article byirradiating the trains of light pulses from the femtosecond laser lightto the work article; and a scattering step of scattering during anetching pause time, from an etching position of the work article, aplasma cloud of an atomic or molecular particle released from the workarticle by the optical ablation caused by the femtosecond laser light atthe etching step, wherein the etching pause time is provided between twotrains of light pulses for a predetermined duration that is longer thana period of irradiating the work article with the train of light pulses.2. A laser etching method according to claim 1, wherein, in irradiatingthe trains of light pulses from the femtosecond laser light to the workarticle, etching is executed by scattering the plasma cloud from theetching position by executing intermittent irradiation to said workarticle with a time interval longer than an oscillation frequency of thepulsed laser.
 3. A laser etching method according to claim 1, wherein,in irradiating said work article with the trains of light pulses fromthe femtosecond laser light, a gas flow is generated to scatter saidplasma cloud from said etching position.
 4. A laser etching methodaccording to claim 3, wherein the gas flow in the etching position ofsaid work article is in an air flow.
 5. A laser etching method accordingto claim 3, wherein the gas flow in the etching position of said workarticle is a nitrogen flow.
 6. A laser etching method according to claim1, wherein in irradiating said work article with the trains of lightpulses from the femtosecond laser light, etching is executed in a mannerthat said femtosecond laser light is irradiated in a state where saidwork article is positioned in a gas that has an atomic weight smallerthan that of a nitrogen molecule.
 7. A laser etching method according toclaim 6, wherein said gas is helium gas.
 8. A laser etching methodaccording to claim 6, wherein said gas is hydrogen gas.
 9. A laseretching method according to claim 1, wherein in irradiating said workarticle with the trains of light pulses from the femtosecond laser,etching is executed in a manner that said femtosecond laser light isirradiated in a state where said work article is positioned in a liquidwhich transmits said femtosecond laser light.
 10. A laser etching methodaccording to claim 9, wherein the liquid transmitting the trains oflight pulses from the femtosecond laser light is water.
 11. A laseretching method according to claim 1, wherein, in irradiating the trainsof light pulses from the femtosecond laser light to said work article,etching is executed by irradiating the femtosecond laser light in astate where said work article is heated to 200° C. or higher to scattersaid plasma cloud from said etching position.
 12. A laser etching methodaccording to claim 1, wherein, in irradiating the trains of light pulsesfrom the femtosecond laser light to said work article, etching isexecuted by irradiating the femtosecond laser light in a state wheresaid work article is provided in a gaseous atmosphere of a pressure notexceeding 10 Torr to scatter the plasma cloud from said etchingposition.
 13. A laser etching method according to claim 1, wherein saidinorganic material is a crystal covalent bond.
 14. A laser etchingmethod according to claim 1, wherein said inorganic material is crystalor amorphous silicon.
 15. A laser etching method according to claim 1,wherein said inorganic material is a silicon compound.